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This invention relates to a system for automatically sharpening the rotating knives of a material cutting or chopping mechanism, and more particularly to a system for automatically sharpening the cutterhead knives of a forage harvester.
With current production forage harvesters, in order to sharpen the knives on the cutterhead, the operator must manually lower the sharpening stone into the knives until he senses that the stone is contacting the rotating knives. The quality, accuracy and uniformity of knife sharpening therefore depends upon the skill and experience of the operator. Some sharpening systems with varying degrees of automation have been proposed, but none have utilized microprocessor technology and therefore, such proposed systems have been functionally limited.
One such system is described in U.S. Pat. No. 4,495,734, issued Jan. 29, 1985 to Rouch. The Rouch system includes a cutter grinding arrangement with a grinding stone carriage which includes a double-acting piston and a control valve therefore. The control valve is operated by a lever which engages abutments at opposite ends of its travel. The grinding stone is moved radially towards the cutterhead by a spindle which is connected to a ratchet wheel which engages a separate pair of abutments. However, this proposed system includes no means for automatically moving the grinding stone away from the cutterhead when knife sharpening is completed. Such a system would be expensive because it requires a double acting cylinder and a hydraulic valve. Furthermore, such a design would have hydraulic lines subject to the stress due to the repetative reciprocal movement of the valve and cylinder to which they are attached.
Another sharpening system has been proposed wherein the stone is moved by electric motors controlled by various limit switches. However, in this system, contact between the stone and the cutterhead is sensed when an electrical circuit is completed due to contact between the cutterhead knives and wires which are embedded in the stone. In such a design, wires must be connected to the movable stone and these wires would be subjected to the stress of repeated flexure due to the repreated motion of the stone. Furthermore, if a wire were to break in such a system, then the system would not detect stone/cutterhead contact and the stone would continue to be driven into the cutterhead past the point of initial contact and catastrophic physical damage could result.
Accordingly, it is desired to have an automatic forage harvester knife sharpening system which utilizes microprocessor technology and which avoids the disadvantages of prior production and proposed systems.